Help with hummmmmmmmmmmm?
Boomzilla -- Sun, 12/06/2009 - 20:41
Well, my McIntosh MC350 finally got back from the repair shop (shipping damage), and yes, it does sound better than the Onkyo receiver that it replaced.
The initial setup was via a passive (unbalanced) preamp into the big Mac. This sounded good with no hum. I then put in a B&K ST5 preamp using the fully-balanced input/output set (expecting an improvement). What I got was a serious background hum! I thought that the balanced interconnections were supposed to reduce noise (including hum)!
Everything in the system plugs into a Monster power strip. Should I reverse the preamp's plug? Dress the wires better? Any ideas appreciated.
Thanks - Boomzilla (unhappily humming along...)
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I would try lifting the grounds on the amp.
By this I mean going from a three-prong AC plug to a two-prong.
If going to two prongs doesn't help, then try selective reversal of the AC plugs.
Last resort - go back to singe-ended cables.
Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications
Hum in an audio system occurs when there are two paths to ground of unequal resistance. The hum is current flow through the ground.
This ground path(s) are through the third prong of a three-prong AC cord. Steven's suggestion is correct; lift the ground of one of the components and you break the ground loop. You must be certain, however, that the system is grounded to earth ground for safety. If high voltage gets on the chassis for some reason, it is shunted to ground, tripping the circuit breaker and preventing a dangerous condition.
I regularly use ground-filter adapters (also called "cheater plugs") on power amplifiers to reduce hum.
Would a ground-fault interrupter circuit work in lieu of a true earth ground?
A good sense of humor makes it ALL sound better!
With the intergration of audio and TV it is common for the floating ground to the ground of the cable company. Every cable spliter has a ground screw which most people dont use. Running a wire and grounding this to the house electric or a cold water pipe will eliminate one source of ground problems.It solved mine and was driving me nuts...love my DVD-A
it might work but if the ground fault interupted is one for the 75 ohm cable wires you might experience some digital glare on your TV.A simple cable ground block from radio shack cat number 15-924 and running the ground to the rear ground screw of your amp will eliminate any floating grounds do to cable. hope this helps asuming your issue is a cable ground issue.this will fix it not bandade it or cause furter problems of a ground interupter.i went that route with problems...happy listening
Robert, I too had a grounfd loop problem ,tried all the tricks cheater plugs, ground fault interuptors , but wasnt happy till i got to the root of the problem.After a bit of reseach i found it to be a problem with the inter face with cable ground and the eletric house ground.A simple cable block ground and a few feet of wire cured the problem. the thought of terminating a Nordost Bramaha cord into a 79c adaptor was killing me.Even though i really couldnt hear an audiable difference.I guess in the end i was afraid of turning the amp on after a shower and getting a shock of my like..lol my best Brian Clarke
Thanks, folks. Steven's suggestion to lift the ground worked perfectly. I first tried reversing the two-prong plug on the preamp - no difference; it still hummed. I then found an old computer power cord (I didn't want to disfigure the heavy-duty McIntosh one without proof of efficacy) and brutally tore off the grounding stud. When I turned on the system again, I could hear only the most faint of background hiss (and I had to have my ear against the grille to hear that). NO HUM!
Thanks for the easy & quick fix. Now, how long must I leave the system on until everything sounds it's best? I understand the thermal stability part (should occur in 30 minutes to an hour), but how long beyond that until the system "burns in?" I have read that some equipment must run for up to a hundred hours until it "opens up." Is this merely hubris on the part of the reviewer, wishing to claim auditory revelations that the casual listener might miss, or is there benefit to leaving equipment on all the time? It would seem that with used equipment, the "burn-in period" would already be complete, or does the process begin anew each time the equipment is shut off & cools down?
Pardon my ignorance here, but I consider youse guys a bit more authoritative than the usual internet blogger... Thanks, also, for your prompt and effective advice.
Cordially - Boomzilla
A good sense of humor makes it ALL sound better!
"Now, how long must I leave the system on until everything sounds it's best?"
Thirty years works for me :)
But for most people (and electronics) You should be pretty well "burned in" after a week of being on 24/7. If you turn your electronics off for several days or more it may take up to an hour for the system to "warm-up" again to the level of performance you are accustomed to. I often turn off the system in my big room for several days at a time and I've come to realize that the first hour it's back on is definitely sub-par compared to the sound after the hour has elapsed.
Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications
OK - I'll leave it on and listen. In the past, I've always turned my system off between listening sessions to avoid vulnerabilities. Lightning strikes and power interruptions (causing a potential speaker-blowing pop on re-energization) have been my concerns. However, if everyone else successfully leaves their systems on 24-7, there's no reason for me not to try. Thanks again for all the good advice!
Boomzilla
A good sense of humor makes it ALL sound better!
"Lightning strikes and power interruptions (causing a potential speaker-blowing pop on re-energization) have been my concerns. "
If you live in an area with a lot of lightning activity (like Florida or Colorado) I would suggest NOT leaving gear plugged in during the storm season.
I diligently unplug during the summer months.
Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications
Thanks again, Steven - Being from Louisiana, I'd surely unplug during hurricanes, but for rapid-developing afternoon thunderstorms (common from about May through October here), I may not be around to unplug. Lots of surge protectors in series, maybe?
A good sense of humor makes it ALL sound better!
I believe that PS Audio has a protection system that allows you to turn off and on circuits via the Internet...
Frankly, in your region I'd just unplug after my evening listening sessions and re-plug in when I got home from work...
Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications
To circle back to the hum problem, a 75 ohm coax CATV cable can cause a ground loop hum if it is connected to a cable box or TV which is plugged into an outlet that is anywhere on the same electrical circuit as the audio system. The TV and the audio system don't have to be connected. This may come up in a home theater set up. I had this problem several years. The TV was plugged into an outlet in another part of the room. There were no interconnects between the TV and the stereo, yet it turned out that the CATV cable was the problem. (My system back then has since evolved into systems, on dedicated lines, etc., but I can stop any time I want to. . .) I tried cheater plugs but they didn't work.
What did work was hooking up an isolation transformer between the 75 coax cable from the wall and the cable box. Jensen Transformers has one specifically for this purpose. I just had a look at the website, www jensentransformers dot com, and the current model is the IsoMax VRD-1FF CATV Isolator. The price hasn't changed from ten years ago, around $60. The hook up is illustrated on the web site. (There are also extremely detailed white papers on all aspects of ground loops.) I have seen similar items from high-end audio companies, at two-three times the price, but I was very happy to find the Jensen and even happier to have a quiet system(!)
But here's a question: Jensen says in its literature, very emphatically, that cheater plugs are unsafe. They say that the ground connection is there for a reason, safety; cheater plugs are actually meant to create a ground connection for 2-prong plugs, not to lift a ground, etc. My dealer had recommended cheater plugs, too, and they are commonly used. What say you? :-)
If the component with the cheater plug is connected via interconnects to a component that is plugged into the wall with a three prong plug, the entire system is grounded to the third-prong earth ground.
Thanks for clarifying -- there had to be an explanation. I hadn't heard of any houses burning down . . . but getting rid of a ground loop hum can be very frustrating.
Darn! I had the preamp and power amp hum-free with the CD input, but when I switched to the DVD input (immediately adjacent on the rear panel), everything began humming again (including the CD input). I tried reversing the AC plug on the DVD player, various combinations of power amp, preamp, and DVD player plugs reversed, and finally went back to unbalanced connections between the preamp and power amp. NOTHING worked - the rig still hummed!
I finally took the preamp back out of the system and went to a passive preamp; the hum stopped.
To summarize here are the following combinations and their results:
CD player, preamp, and ungrounded power amp = no hum (DVD player was NOT powered on at time)
DVD player, preamp, and ungrounded power amp = HUM (CD player remained powered on at time)
CD player, preamp, and grounded power amp = HUM (DVD player was NOT powered on at time)
CD player and grounded power amp only (passive preamp) = NO HUM (DVD player was NOT powered on at time)
DVD player and ungrounded power amp only (passive preamp) = NO HUM (CD player remained powered on at time)
As best as I can figure, there is a ground interaction between something and the preamp. Without the preamp in the system, I get no hum anywhere even with both the CD and DVD players powered on. The preamp has a two-prong, ungrounded AC plug (as do both the CD and DVD players). The power amp has a three-prong, grounded plug, although it is currently running without the ground wire connected. The passive preamp isolates the grounds of its inputs. In other words, when one source is connected, the other sources are completely electrically isolated - there is no common ground except between the live source and the outputs.
I'd really like to use the preamp, since it gives remote volume capabilities, but the hum is really loud. The only other variable that might be relevant is that all components are plugged into a Monster Cable surge suppressor strip. I haven't tried removing the strip yet, although if it is working properly, it shouldn't (in theory) be capable of creating a ground loop itself. Again, any hum-reduction suggestions are appreciated. I'm getting really tired of the hum gremlin. Thanks!
A good sense of humor makes it ALL sound better!
Did you try what i said??? DVD player on and problem continued?? sounds like the ground loop problem is due to cable ground buy one of those cable grounding blocks and run the wire from the block to a ground on the back of you amp or run the wire directly into the ground wire in the electrical outlet Its a $5 fix...i tried all the 2 prong approachs but it only a bandade.seemed stupid to have $1500 nordost power cables terminated with a 79c pug..cure the ground loop will fix it for ever did with my system cary tube amps and aesoteric DVD A player
No, Brian, I never tried what you said. Why? Because there is NO cable hookup in this system ANYWHERE... The DVD player (when it's playing movies) is hooked up directly to a video projector. The audio output from the DVD player goes directly into the stereo system. No cable anywhere - but I appreciate the suggestion.
A good sense of humor makes it ALL sound better!
My troubleshooting method for this problem would be:
1. start with only the pre and amp connected via balanced.
2. check for hum on any and all inputs.
3. connect one input device, check for hum.
4. if OK add a second, check for hum.
5. when you connect the input device that causes hum then disconnect all other input devices to see if hum changes or goes away.
6. You are looking for the two devices that TOGETHER are creating the ground loop.
Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications
Mine was slightly different:
1. start with the humming preamp and sell it
2. get a preamp of the same make as the power amp
3. if they still hum, sell them both and buy an integrated amp
Boomzilla
A good sense of humor makes it ALL sound better!
ROTFL!!!
And if the integrated amp hums get a dixie cup and a string...
Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications
LMAO - Been there, Done that...
A good sense of humor makes it ALL sound better!